Electromagnetic actuator

ABSTRACT

The present invention relates to an improvement in an electromagnetic actuator which is composed of a yoke, a stationary core fixed to the yoke, a movable core capable of reciprocally moving with respect to the stationary core, a coil wound around the movable core for applying the first magnetic flux thereto when the coil is energized, and a permanent magnet fixed to the yoke or the movable core so as to apply the second magnetic flux which dividingly flows to the first magnetic flux in parallel thereto. This improved electromagnetic actuator is characterized that it satisfies the condition (a); 
     
         (a) 0.5&gt;R.sub.1 /R.sub.0 &gt;0 
    
     wherein, 
     R 1  represents the magnetic reluctance of the magnetic pass of one divided magnetic flux generated by the permanent magnet, including the magnetic reluctance of the gap d 1  between one pole face of the movable core and one pole face of the yoke; 
     R 2  represents the maganetic reluctance of the magnetic pass of the other divided magnetic flux generated by the permanent magnet, including the magnetic reluctance of the gap d 2  between the other pole face of the movable core and one pole face fo the stationary core; and 
     
         R.sub.2 =R.sub.1 +R.sub.2 
    
     So the acutator can provide a high sensitivity and a great actuating force with using a low current and can be applied to a electromagnetic valve and the like.

TECHNICAL FIELD

The present invention relates to an electromagnetic actuator which isused for specific devices such as electromagnetic valves,electromagnetic pumps, electromagnetic locking devices, electromagnetrelays, electromagnetic clutches, and so on which canelectromagnetically control a holding operation of a mechanical stablestate and a shifting operation from such mechanical stable state.

BACKGROUND TECHNICS OF THE INVENTION

Generally, commonly used electromagnetic valves and the like havecontained the electromagnetic actuator as shown in FIG. 10. Such typeelectromagnetic actuator comprises a stationary core 1 fixed on a yoke2, movable core 3 movably arranged with respect to the stationary core 1so as to reciprocally move in the direction represented by the arrow 11,and coil 7 wound around the movable core 3 to generate the firstmagnetic flux 8 when the coil 7 is energized.

However, this type electromagnetic actuator is relatively poor in itssensitivity and thus can not generate required attractive force at a lowcurrent. The inventor of the present invention has already proposedimproved electromagnetic actuators which can generate great moving forcein spite of low current. This type electromagnetic actuators have beenshown in PCT/JP84/00084, PCT/JP85/00313, PCT/JP85/00314, andPCT/JP85/00536.

This type of electromagnetic actuator further comprise a permanentmagnet 5 in addition to the conventional device as shown in FIG. 10. Indetail, as shown in FIG. 1 to FIG. 4, the permanent magnet 5 is securedto the yoke 2 or the movable core 3 so as to generate the secondmagnetic flux 9 which dividingly flows in parallel to the first magneticflux 8 generated by the coil 7.

In the previously invented devices shown in FIG. 1, FIG. 2 and FIGS.3(a), (b), the movable core 3 is reciprocally moved in the directionrepresented by the arrow 11 with respect to the stationary core 1.

In the previously invented device shown in FIG. 4(a) and FIG. 4(b), themovable core 3 is secured to a shaft 13a and can be rotatably moved inthe direction represented by the arrow 11 with respect to the stationarycore 1 through a journal 13b.

However, the above described devices shown in FIG. 1 to FIG. 4,previously proposed by the inventor of the present invention, can notalways provide characteristics of a high sensitivity since it depends onthe combination of values such as magnetomotive forces caused by thecoil 7 and the permanent magnet 5 and magnetic reluctances of thepermanent magnet 5 and in the gap between the movable core 3 and thestationary core 1 or the movable core 3 and the yoke 2.

DESCRIPTION OF THE INVENTION

Thererfore, in order to overcome the above mentioned problems, it is anobject of the present invention to easily provide an improvedelectromagnetic actuator which can provide a high sensitivity and agreat actuating force with using a low current.

The present invention is based on the following knowledges according tovarious experiments and theoretical analysis.

First of all, arithmetic operation on the magnetic circuits ofconventional devices, previously proposed by the inventor of the presentinvention, shown in FIG. 5 and FIG. 6 will be conducted.

In these drawings, a stationary core 1 is installed in a yoke 2 withfixing to the inside of the yoke 2. A movable core 3 is so arranged asto be capable of reciprocating in the direction represented by the arrow11 with respect to the stationary core 1. A first gap d₁ is definedbetween a pole face 2a of the yoke 2 and a pole face 3a of the movablecore 3. A second gap d₂ is also defined between a pole face 1a of thestationary core 1 and a pole face 3b of the movable core 3.

A permanent magnet 5 is fixed on the inner wall of the yoke 2. Indetail, its S-pole face is fixed on the inner wall and its N-pole facefaces to the movable core 3 through a gap g.

Assuming that the first magnetic flux 8 generated when a coil 7 isenergized by the current as shown in the drawings and the secondmagnetic fluxes 9a and 9b, dividingly flowed in parallel to the firstmagnetic flux 8, generated by the permanent magnet 5 are wholly passedthrough the gaps d₁ and d₂, the equivalent magnetic circuits of thedevices shown in FIG. 5 and FIG. 6 are represented by the circuitdiagram in FIG. 7.

Although the electromotive force F₁ of the equivalent magnetic circuitsof the devices shown in FIG. 5 and FIG. 6 is located in the positionmarked by the dotted line in FIG. 7 and FIG. 9, this arithmeticoperation will be performed on the assumption that the position of F₁corresponds to that of F_(o) as a matter of convenience.

The parameters used in this arithmetic operation are as follows.

F_(o) ; Magnetomotive force generated when the coil 7 is energized.

F_(p) ; Magnetomotive force generated by the permanent magnet 5.

S; Sectional area of the gaps d₁ and d₂.

S_(p) ; Sectional area of the gap g.

L_(p) ; Length of magnetizing direction caused by the permanent magnet5.

μ_(o) ; Permeability of the gaps d₁ and d₂.

μ_(r) ; Reversible permeability of the permanent magnet 5.

R₁ ; Magnetic reluctance of the magnetic pass of one devided magneticflux 9a generated by the permanent magnet 5, including magneticreluctance of the gap d₁ =(d₁ /μ_(o))S.

R₂ ; Magnetic reluctance of the magnetic pass of the other dividedmagnetic flux 9b generated by the permanent magnet 5, including themagnetic reluctance of the gap d₂ =(d₂ /μ_(o))S.

R_(p) ; Magnetic reluctance of the permanent magnet 5=(L_(p)/μ_(r))S_(p).

In these parameters, the magnetic reluctance (g/μ_(o))S_(p) of the gap gis contained in the magnetic reluctance R_(p).

Now, in order to independently obtain the first magnetic flux 8generated when the cil 7 is energized, and the second magnetic fluxes 9aand 9b generated by permanent magnet 5, the circuit shown in FIG. 7 isapplied with the principle of superposition.

First of all, the second magnetic fluxes 9a and 9b are obtained in thefollowing manner.

If the second magnetic fluxes 9a and 9b passing through the gaps d₁ andd₂ in the equivalent circuit shown in FIG. 8 are respectivelyrepresented by φ₁ and φ₂, the following quadratic equations will beestablished.

    F.sub.p =R.sub.p (φ.sub.1 +φ.sub.2)+R.sub.1 φ.sub.1 ( 1)

    R.sub.1 φ.sub.1 =R.sub.2 φ.sub.2                   ( 2)

According to the equations (1) and (2),

    φ.sub.1 =(R.sub.2 F.sub.p)/{R.sub.p (R.sub.1 +R.sub.2)+R.sub.1 +R.sub.2 }                                                         (3)

    φ.sub.2 =(R.sub.1 F.sub.p)/{R.sub.p (R.sub.1 +R.sub.2)+R.sub.1 R.sub.2 }(4)

Nextly, the first magnetic flux 8 generated by the coil 7 is obtained asfollows.

If the magnetic flux passing through the permanent magnet 5 isrepresented by φ₄ ad the magnetic flux passing the gap d₂ is representedby φ₃ in the equivalent circuit shown in FIG. 9, the following equation(5) will be established.

    F.sub.o =(R.sub.1 +R.sub.2)φ.sub.3 +R.sub.1 φ.sub.4 ( 5)

    R.sub.p φ.sub.4 =R.sub.2 φ.sub.3                   ( 6)

These equations are rearranged to obtain the values of φ₃ and φ₄.

    φ.sub.3 =(R.sub.p F.sub.o)/{(R.sub.1 +R.sub.2)R.sub.p +(R.sub.1 R.sub.2)}                                                 (7)

    φ.sub.4 =(R.sub.2 F.sub.o)/{(R.sub.1 +R.sub.2)R.sub.p +(R.sub.1 R.sub.2)}                                                 (8)

At the next step, the arithmetic operation will be conducted on theelectromagnetic force P applied to the movable core 3.

The electromagnetic force P applied to the movable core 3 of theelectromagnetic actuator shown in FIG. 5 is generated in only the gapd₁, and the electromagnetic force P is generated in both the gaps d₁ andd₂ of the bistable type electromagnetic actuator shown in FIG. 6. Thevalue of the electromagnetic force P is proportion to the square of themagnetic flux passing through the gaps d₁ and d₂. This relation isexpressed by the following equation.

    P=φ.sup.2 /(2μ.sub.o S)                             (9)

wherein,

P; the electromagnetic force applied to the movable core 3.

φ; the magnetic flux passing through the gaps d₁ and d₂.

Accordingly the above equations (4), (7) and (9), the force representedby P_(s) applied to the movable core 3 of the monostable typeelectromagnetic actuator shown in FIG. 5 is obtained by the followingequation;

    P.sub.s ={1/(2μ.sub.o S)}[(R.sub.1 F.sub.p +R.sub.p P.sub.o)/{R.sub.p (R.sub.1 +R.sub.2)+R.sub.1 R.sub.2 }].sup.2               ( 10)

Further, according to the above equations (3), (4), (7), (8) and (9),the force represented by P_(d) applied to the movable core 3 of thebistable type electromagnetic actuator shown in FIG. 6 is obtained bythe following equation wherein the magnetic fluxes passing through thegaps d₁ and d₂ respectively represented by φd₁ and φd₂ ; ##EQU1##wherein, the magnetic flux φd₁ passing through the gap d₁ is expressedby the equation;

    φd.sub.1 =φ.sub.1 -φ.sub.4 - .sub.3,

and the magnetic flux φd₂ passing through the gap d₂ is expressed by theequation;

    φd.sub.2 =φ.sub.2 +φ.sub.3.

The direction of the forces P, P_(s), and P_(d) making the movable core3 move rightwards in the drawings represents the positive direction.

Another conventional device shown in FIG. 10 has the same values of thesectional area of the movable core 3, the length of the gaps d₁ and d₂,and the magnetomotive force generated by the coil 7 when it is energizedas the conventional devices shown in FIG. 5 and FIG. 6, previouslyproposed by the inventor of the present invention. The arithmeticoperation wil be also executed on these conventional devices in order tocompare the forces applied to the movable cores 3 in the respectivedevices.

The magnetic reluctance R_(o), the magnetic flux φ_(o), and the forceP_(o) applied to the movable core 3 of the conventional device shown inFIG. 10 are respectively represented by the following equations.##EQU2##

According to the equations (10), (11), and (14), the ratio of the forcesapplied to the respective movable cores 3 when the coils 7 of therespective devices are energized in the manner shown in the drawings isrepresented by the following equations. ##EQU3##

In order to form the normalization grasp with respect to the equations(15) and (16), the parameters from them should be selected.

The values of the magnetic reluctances R₁, R₂ and R_(p) are divided, bythe value of the magnetic reluctance R_(o) to form non-dimensionalformulae as follows. ##EQU4## Wherein, "d" is represented by theequation d₁ +d₂.

In order to obtain the parameter representing the size of the permanentmagnet 5, both sides of the equation φ_(p) =F_(p) /R_(p) arerespectively divided by the basic magneic flux φ_(o) =F_(o) /R_(o) asfollows.

    φ.sub.p /φ.sub.o =(R.sub.o F.sub.p)/(R.sub.p F.sub.o) (20)

Then the equations (17), (18) and (20) are substituted into theequations (15) and (16), and rearranged as follows. That is, theserearranged equations can represent the value of the force applied to themovable core 3 of the electromagnetic actuator in the normalizationgraph which employs two parameters of φ_(p) /φ_(o) and R_(p) /F_(o) anda variable d₁ /d(≈R₁ /R_(o)). ##EQU5##

Wherein, the magnetic reluctance R_(p) of the permanent magnet 5 is ininverse proportion to its reversible permeability μ_(r) and inproportion to the length of magnetizing direction caused by thepermanent magnet 5.

Here the value of the reversible permeability μ_(r) is approximate tothe permeability μ_(o) in a vacuum. Accordingly, if the sectional areaS_(p) of the gap "g" is equivalent to S, the equation (19) is rearrangedand thus the following equation will be established.

    R.sub.p /R.sub.o ≈L.sub.p /d

Although in an ordinary way the valve of L_(p) is greater than that of"d", we will discuss on the value of R_(p) /R_(o) within the range of1/3 to 1/4.

If the intensity of magnetization of the permanent magnet 5 isrepresented by J_(p) and the magnetic flux density B caused by the coil7 in the energized state, the following equation will be established.

    Φ.sub.p /Φ.sub.o =(J.sub.p S.sub.p)/(B·S)

The value of J_(p) depends on the material for the magnet such as 0.4(T)for a ferrite magnet, 0.8(T) for a casting magnet, 1.0(T) for a rareearth magnet and so on. Thus the value of Φ_(p) /Φ_(o) is variable.Although, we will discuss on the range from 0.5 to 4.

As mentioned above, the electromagnetic force applied to the movablecore 3 of the monostable type electromagnetic actuator shown in FIG. 5is represented by the equation (21) with ignoring leakage flux. As shownin the graphs in FIG. 11(a), FIG. 11(b), FIG. 11(c), FIG. 11(d), thevalue of P_(s) /P_(o) with respect to various values of Φ_(p) /Φ_(o) canbe calculated with taking the values of R_(p) /R_(o) as the parameterand the values of R₁ /R_(o) as the variable.

Also the electrmagnetic force applied to the movable core 3 of thebistable type electromagnetic actuator shown in FIG. 6 can be calculatedby equation (22). The resulted values are shown in the graphs in FIG.12(a), FIG. 12(c) and FIG. 12(d).

According to the resulted values from the graphs in FIG. 11(a), FIG.11(b), FIGS. 11(c) and 11(d) and FIG. 12(a), FIG. 12(b), FIG. 12(c) andFIG. 12(d), and the results from various tests on the trial device ofthe present invention, the following condition is always required to bevalid for the condition that the value of P_(s) /P_(o) or P_(d) /P_(o)is greater than 1; that is, the electromagnetic force applied to themovable core 3 of the electromagnetic actuator shown in FIG. 5 or FIG. 6previously proposed by the inventor is greater than that of conventionalelectroagnetic actuator shown in FIG. 10.

    (a) 0.5>R.sub.1 /R.sub.o >0

Further, if the following condition (b) is satisified in addition to thecondition (a), a higher sensitive property will be obtained.

    (b) φ.sub.p /φ.sub.o >0.5

Also if the following condition (c) is satisfied in addition to theconditions (a) and (b), a furthermore high sensitive property will beobtained.

    (c) R.sub.p /R.sub.o >0.25

The present invention has been achieved in accordance with the abovementioned knowledge. In detail, the present invention relates to animprovement in electromagnetic actuator which is composed of a yoke, astationary core fixed to the yoke, a movable core capable ofreciprocally moving with respect to the stationary core, a coil woundaround the movable core for applying the first magnetic flux theretowhen the coil is energized, and a permanent magnet fixed to the yoke orthe movable core so as to apply the second magnetic flux whichdividingly flows to the first magnetic flux in parallel thereto.Therefore, it is an object of the present invention to provide animproved electromagnetic actuator which can satisfy the condition (a).

    (a) 0.5>R.sub.1 /R.sub.o >0

Wherein, R₁ represents the magnetic reluctance of the magnetic pass ofone divided magnetic flux generated by the permanent magnet, includingthe magnetic reluctance of the gap d₁ between one pole face of themovable core and one pole of the yoke;

R₂ represents the magnetic reluctance of the magnetic pass of the otherdivided magnetic flux generated by the permanent magnet, including themagnetic reluctance of the gap d₂ between the other pole face of themovable core and one pole face of the stationary core; and

    R.sub.o =R.sub.1 +R.sub.2

As explained above, the device according to the present invention canprovide superior effects that a great actuating force can be alwaysgenerated by consuming an extremely low current since the values of themagnetic reluctance and magnetotive force and so on in its magneticcircuit can be restricted within a predetermined range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration for explaining the conventionaldevice previously proposed by the inventor of the present invention andthe first embodiment of the present invention;

FIG. 2 is a schematic illustration for explaining the conventionaldevice previously proposed by the inventor of the present invention andthe second embodiment of the present invention;

FIG. 3 is a schematic illustration for explaining the conventionaldevice previously proposed by the inventor of the present invention andthe third embodiment of the present invention;

FIG. 4(a) and FIG. 4(b) are schematic views for explaining theconventional device previously proposed by the inventor of the presentinvention and the fourth embodiment of the present invention, whereinFIG. 4(a) is a sectional view taken along the line A--A in FIG. 4(b);

FIG. 5 and FIG. 6 are schematic views for explaining the conventionaldevices previously proposed by the inventor of the present invention;

FIG. 7, FIG. 8 and FIG. 9 are circuit diagrams showing equivalentmagnetic circuits;

FIG. 10 is a schematic view for explaining the conventional device;

FIG. 11(a), FIG. 11(b), FIG. 11(c) and FIG. 11(d) are the tables andgraphs for explaining electromagnetic force generated by theconventional device shown in FIG. 5; and

FIG. 12(a), FIG. 12(b), FIG. 12(c) and FIG. 12(d) are tables and graphsfor explaining electromagnetic force generated by the conventional shownin FIG. 6.

FIGS. 13a and 13b are schematic views for explaining the invention inwhich a permanent magnet is fixed to the movabe core.

THE BEST MODE FOR EMBODYING THE PRESENT INVENTION

Hereinafter, the present invention will be explained in detail accordingto the embodiments in conjunction with the accompanying drawings.

The embodiments according to the present invention have thesubstantially same structure as the conventional devices shown in FIG. 1to FIG. 4 except for the following points.

The embodiments are so designed as to satisfy the condition defined bythe eqation (a):

    0.5>R.sub.1 /R.sub.o >0

wherein,

R₁ represents the magnetic reluctance of the magnetic pass of onedivided magnetic flux 9a generated by the permanent magnet 5, includingthe magnetic reluctance of the gap d₁ between one pole face of themovable core and one pole face of the yoke;

R₂ representes the magnetic reluctance of the magnetic pass of the otherdivided magnetic flux 9b generated by the permanent magnet 5, includingthe magnetic reluctance of the gap d₂ between the other pole face of themovable core and one pole face of the stationary core; and

    R.sub.o R.sub.1 +R.sub.2

Further, the following condition (b) is satisfied in addition to thecondition (a), a higher sensitive property will be obtained.

    (b) φ.sub.p /φ.sub.o >0.5

wherein

R_(p) represents the magnetic reluctance of the premanent magnet;

F_(o) represents the magnetomotive force caused by energizing the coil;

and F_(p) represents the magnetomotive force caused by the permanentmagnet.

wherein,

φ_(o) represents the magnetic flux caused by energizing the coi; and

φ_(p) equals to R_(o) F_(p) /R_(p) F_(o).

Also if the folowing condition (c) is satisfied in addition to theconditions (a) and (b), a furthermore high sensitive property will beobtained.

In order to satisfy these conditions formulae the current for energizingthe coil 7 of the winding number thereof may be suitably adjusted; thelength between N and S poles of the permanent magnet 5 may be adjusted;the perment 5 per se such as material, figure, or the like may beselected; the magnetic pole faces of the stationary core, the yoke andthe movable core may be meltingly covered or plated with a non-magneticmaterial layer; and/or the distace of the gaps d₁ and d₂ may bedadjusted by cutting work.

AVAILABILITY IN INDUSTRIAL FIELD

The present invention can be applied to the device whichelectromagnetically controls a holding operation of a mechanical stablestate and a shifting operation from the mechanical stable state; forexample, electromagnetic valve, electromagnetic pump, electromagneticlocking device, electromagnetic relay, electromagnetic clutch, and thelike.

I claim:
 1. An electromagnetic actuator which is composed of a yoke, astationary core fixed to the yoke, a movable core capable ofreciprocally moving with respect to the stationary core, a coil woundaround the movable core for applying the first magnetic flux theretowhen the coil is energized, and a permanent magnet fixed to the yoke soas to apply the second magnetic flux which dividingly flows to the firstmagnetic flux in parallel thereto; wherein the improvement ischaracterized that this electromagnetic actuator satisfies the condition(a);

    (a) 0.5>R.sub.1 /R.sub.o >0

wherein, R₁ represents the magnetic reluctance of the magnetic pass ofone divided magnetic flux generated by the permanent magnet, includingthe magnetic reluctance of the gap d₁ between one pole face of themovable core and one pole face of the yoke; R₂ represents the magneticreluctance of the magnetic pass of the other divided magnetic fluxgenerated by the permanent magnet, including the magnetic reluctance ofthe gap d₂ between the other pole face of the movable core and one poleface of the stationary core; and

    R.sub.o =R.sub.1 +R.sub.2.


2. The electromagnetic actuator as set forth in claim 1 furthersatisfying the following condition (b);

    (b) φ.sub.p /φ.sub.o >0.5

wherein, φ_(o) represents the magnetic flux caused when the coil isenergized; and φ_(p) equals to R_(o) F_(p) /R_(p) F_(o) wherein, R_(p)represents the magnetic reluctance of the permanent magnet; F_(o)represents the magnetomotive force caused when the coils energize; andF_(p) represents the magnetomotive force caused by the permanent magnet.3. The electromagnetic actuator as set forth in claim 2 furthersatisfying the following condition (c):

    (c) R.sub.p /R.sub.o >0.25.


4. An electromagnetic actuator which is composed of a yoke, a stationarycoke fixed to the yoke, a movable core capable of reciprocally movingwith respect to the stationary core, a coil wound around the movablecore for applying the first magnetic flux thereto when the coil isenergized, and a permanent magnet flux which dividingly flows to thefirst magnetic flux in parallel thereto; wherein the improvement ischaracterized; that this electromagnetic actuator satisfies thecondition (a);

    (a) 0.5>R.sub.1 R.sub.o >0

wherein, R₁ represents the magnetic reluctance of the magnetic pass ofone divided magnetic flux generated by the permanent magnet, includingthe magnetic reluctance of the gap d₁ between one pole face of themovable core and one pole face of the yoke; R₂ represents the magneticreluctance of the magnetic pass of the other divided magnetic fluxgenerated by the permanent magnet, including the magnetic reluctance ofthe gap d₂ between the other pole face of the movable core and one poleface of the stationary core; and

    R.sub.o =R.sub.1 +R.sub.2.